In certain situations, where power is to be transferred from, for example, a microwave generator to an antenna, it is of interest to change from one waveguide mode to one or more other modes. With power generation in certain microwave generators, the power is delivered typically in a so-called TM01 mode in a circular waveguide. For a more detailed description of the mode type, refer to “Balanis, Advanced Engineering Electromagnetics, Wiley 1989”. This mode is often not suitable for exciting an antenna, for example of the waveguide horn type, due to the fact that it gives a toroidal radiation pattern with a zero depth in the axial direction of the waveguide. In many situations, it is therefore of interest to deliver the power in a circular waveguide in TE11 mode. If linear polarization is of interest, the power is delivered accordingly in one TE11 mode. For the generation of circular polarization in an antenna, the power can be delivered in two orthogonal TE11 modes excited 90 degrees out of phase in time.
Conversion of TM01 mode to TE11 mode is known in connection with the exciting of antennas, see for example U.S. Pat. No. 4,999,591. The mode converter described in this document has limitations regarding polarization and can be difficult to manufacture with precision due to its asymmetrical design.
Mode converters for converting power from the circular so-called TM01 mode to one or two TE11 modes are difficult to achieve, particularly if they are to cope with high power.